In accordance with the admixture theory of the exocrine pancreatic secretion a linear relation between concentrations of bicarbonate and protein in the pancreatic juice is to be expected.2. Pancreatic juice was obtained through a Thomas cannula in three unanaesthetized dogs during digestion of a meal.3. The actual concentration of bicarbonate and protein showed a good approximation to a straight-line relation.4. The calculated concentration of bicarbonate in the distal secretion was nearly identical with the highest concentration of bicarbonate obtained in the pancreatic juice after stimulation with secretin.